This invention relates generally to controlling the operation of equipment for processing materials to produce an aggregate product having a predetermined weight ratio of particle sizes. In a preferred embodiment of the invention, the gradation of a sample of a crushed stone product is automatically analyzed and the results of such analysis are used to control the operation of the crusher or crushers.
Analysis of products comprised of various aggregate materials is commonly required in the construction, mining and aggregate processing industries to insure that the materials meet the required specifications for quality, composition and/or gradation. Many such aggregate products are comprised of mixtures or blends of components having various particle sizes. Thus, for example, certain coal and coke products and industrial catalytic powders are sold having various particle sizes in specified ranges by weight. Crushed stone products that are used in the construction of roadways may also include mixtures or blends of several particle sizes in various specified ranges, depending on the anticipated use. Several such crushed stone products, as well as sand and/or other aggregates and other additives are combined in specific weight percentages in the manufacture or processing of bituminous paving mixtures.
Samples of these aggregate products may be taken at various stages during the processing or manufacturing thereof for analysis to insure that the proper particle sizes are being produced. Such samples may be taken from conveyors or other transport devices, or from product stockpiles, silos or other storage facilities. Such samples may be taken manually or automatically, and they may be taken from aggregate products produced by batch or continuous processes.
It is known, for example, that the particle size distribution in a quantity of aggregate materials may be determined more-or-less automatically. Thus, for example, U.S. Pat. No. 3,439,800 of Tonjes, U.S. Pat. No. 5,059,310 of Fischer et al. and U.S. Pat. No. 5,222,605 of Pogue describe methods and devices for automatically determining the proportionate amounts of various particle sizes of such a product. Such methods and devices are typically used to determine if a sample of an aggregate product meets required specifications for particle size distribution. However, it would be desirable if a sampling method and apparatus could be developed that could control the crushers or other equipment that is employed in processing or manufacturing the product. It would also be desirable if such a method and apparatus could be developed that would provide quicker and more accurate analysis of the gradation of a sample.
Among the advantages of the invention is that it provides a system that may be used in automatically controlling the processing or manufacturing of an aggregate product based upon the analysis of the particle size distribution of a sample of the product. Another advantage of the invention is that it includes a gradation assembly that may be vibrated in such a way as to provide a quick, accurate and efficient analysis of the particle size distribution of a sample.
Additional objects and advantages of this invention will become apparent from an examination of the drawings and the ensuing description.
As used herein, aggregate materials refers to materials that are produced and/or sold in particulate form with or without other additives, such as, for example, crushed limestone and other types of crushed stone, bituminous paving mixtures such as hot-mix asphalt and cold mix, gravel, sand, lime, coal, coke, metallic oxide and other powders used for catalytic or other reactive purposes, and similar materials.
As used herein, a product which includes aggregate materials of various particle sizes in a predetermined weight ratio refers to a product comprised of one or more aggregate materials having a plurality of particle sizes in a predetermined ratio by weight.
The invention comprises a system for controlling the production of a product which includes aggregate materials of various particle sizes in a predetermined weight ratio. More specifically, the invention comprises a system for controlling the operation of an item of equipment, such as a crusher, for processing materials to produce such a product. The system includes a sampling device for obtaining a sample of the product from a predetermined location and a gradation assembly. The gradation assembly includes a plurality of gradation screens and a weighing pan that is adapted for measuring the weight of aggregate material. The gradation screens are supported by a frame in a generally horizontal attitude in a stacked arrangement, so that each screen in the stack has screen openings that are smaller than those of the screen immediately above it in the stack. The assembly also includes means for vibrating the screens and means for sequentially depositing the aggregate material that is retained on each screen or that passes through all of the screens in the weighing pan. Means are also provided for determining the ratios of the weights of the amounts of the aggregate materials that are retained on each of the screens or that passes through all of the screens to the total weight of the sample, and means for determining if each of the ratios of the weights of the amounts of the aggregate materials that are retained on each of the screens or that passes through all of the screens to the total weight of the sample meets a predetermined standard. The system also includes means for adjusting the operation of the item of equipment if the ratio of the weight of the aggregate materials that are retained on any of the screens or that passes through all of the screens to the total weight of the sample fails to meet the predetermined standard.